/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.extensions.euphoria.core.client.operator;



import com.bff.gaia.unified.sdk.extensions.euphoria.core.annotation.audience.Audience;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.annotation.operator.Basic;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.annotation.operator.StateComplexity;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.functional.ExtractEventTime;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.functional.UnaryFunctor;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.io.Collector;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.operator.base.Builders;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.operator.base.Operator;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.operator.hint.OutputHint;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.type.TypeAware;

import com.bff.gaia.unified.sdk.extensions.euphoria.core.translate.OperatorTransform;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.values.PCollection;

import com.bff.gaia.unified.sdk.values.PCollectionList;

import com.bff.gaia.unified.sdk.values.TypeDescriptor;

import com.bff.gaia.unified.vendor.guava.com.google.common.base.MoreObjects;

import org.joda.time.Duration;



import javax.annotation.Nullable;

import java.util.Optional;



import static java.util.Objects.requireNonNull;



/**

 * A transformation of a dataset from one type into another allowing user code to generate zero,

 * one, or many output elements for a given input element.

 *

 * <p>The user supplied map function is supposed to be stateless. It is fed items from the input in

 * no specified order and the results of the map function are "flattened" to the output (equally in

 * no specified order.)

 *

 * <p>Example:

 *

 * <pre>{@code

 * PCollection<String> strings = ...;

 * PCollection<Integer> ints =

 *        FlatMap.named("TO-INT")

 *           .of(strings)

 *           .using((String s, Context<String> c) -> {

 *             try {

 *               int i = Integer.parseInt(s);

 *               c.collect(i);

 *             } catch (NumberFormatException e) {

 *               // ~ ignore the input if we failed to parse it

 *             }

 *           })

 *           .output();

 * }</pre>

 *

 * <p>The above example tries to parse incoming strings as integers, silently skipping those which

 * cannot be successfully converted. While {@link Collector#collect(Object)} has been used only once

 * here, a {@link FlatMap} operator is free to invoke it multiple times or not at all to generate

 * that many elements to the output dataset.

 *

 * <h3>Builders:</h3>

 *

 * <ol>

 *   <li>{@code [named] ..................} give name to the operator [optional]

 *   <li>{@code of .......................} input dataset

 *   <li>{@code using ....................} apply {@link UnaryFunctor} to input elements

 *   <li>{@code [eventTimeBy] ............} change event time characteristic of output elements

 *       using {@link ExtractEventTime}

 *   <li>{@code output ...................} build output dataset

 * </ol>

 */

@Audience(Audience.Type.CLIENT)

@Basic(state = StateComplexity.ZERO, repartitions = 0)

public class FlatMap<InputT, OutputT> extends Operator<OutputT>

    implements TypeAware.Output<OutputT> {



  /**

   * Starts building a nameless {@link FlatMap} operator to transform the given input dataset.

   *

   * @param <InputT> the type of elements of the input dataset

   * @param input the input data set to be transformed

   * @return a builder to complete the setup of the new {@link FlatMap} operator

   * @see #named(String)

   * @see OfBuilder#of(PCollection)

   */

  public static <InputT> UsingBuilder<InputT> of(PCollection<InputT> input) {

    return named(null).of(input);

  }



  /**

   * Starts building a named {@link FlatMap} operator.

   *

   * @param name a user provided name of the new operator to build

   * @return a builder to complete the setup of the new {@link FlatMap} operator

   */

  public static OfBuilder named(@Nullable String name) {

    return new Builder<>(name);

  }



  // ------------- Builders chain



  /** Builder exposing {@link #of(PCollection)} method. */

  public interface OfBuilder extends Builders.Of {



    @Override

    <InputT> UsingBuilder<InputT> of(PCollection<InputT> input);

  }



  /**

   * A builder which allows user to determine {@link FlatMap FlatMap's} {@link UnaryFunctor

   * functor}.

   *

   * @param <InputT> Input elements type parameter.

   */

  public interface UsingBuilder<InputT> {



    /**

     * Specifies the user defined map function by which to transform the final operator's input

     * dataset.

     *

     * @param <OutputT> the type of elements the user defined map function will produce to the

     *     output dataset

     * @param functor the user defined map function

     * @return the next builder to complete the setup of the {@link FlatMap} operator

     */

    <OutputT> EventTimeBuilder<InputT, OutputT> using(UnaryFunctor<InputT, OutputT> functor);



    <OutputT> EventTimeBuilder<InputT, OutputT> using(

		UnaryFunctor<InputT, OutputT> functor, TypeDescriptor<OutputT> outputTypeDescriptor);

  }



  /**

   * Builder allowing user to specify how event time is associated with input elements.

   *

   * @param <InputT> input elements type

   * @param <OutputT> output elements type

   */

  public interface EventTimeBuilder<InputT, OutputT> extends Builders.Output<OutputT> {



    /**

     * Specifies a function to derive the input element's event time. Processing of the input stream

     * continues then to proceed with this event time.

     *

     * @param eventTimeFn the event time extraction function

     * @return the next builder to complete the setup of the {@link FlatMap} operator

     */

    default Builders.Output<OutputT> eventTimeBy(ExtractEventTime<InputT> eventTimeFn) {

      // allowed timestamp shifts to infitive past

      return eventTimeBy(eventTimeFn, null);

    }



    /**

     * Specifies a function to derive the input element's event time. Processing of the input stream

     * continues then to proceed with this event time.

     *

     * @param eventTimeFn the event time extraction function

     * @param timestampSkew allowed skew in milliseconds of already assigned timestamps and the

     *     newly assigned (see {@link DoFn#getAllowedTimestampSkew}

     * @return the next builder to complete the setup of the {@link FlatMap} operator

     */

    Builders.Output<OutputT> eventTimeBy(

		ExtractEventTime<InputT> eventTimeFn, @Nullable Duration timestampSkew);

  }



  /** Builder of {@link FlatMap}. */

  public static class Builder<InputT, OutputT>

      implements OfBuilder,

          UsingBuilder<InputT>,

          EventTimeBuilder<InputT, OutputT>,

          Builders.Output<OutputT> {



    @Nullable private final String name;

    private PCollection<InputT> input;

    private UnaryFunctor<InputT, OutputT> functor;

    @Nullable private TypeDescriptor<OutputT> outputType;

    @Nullable private ExtractEventTime<InputT> evtTimeFn;

    private Duration allowedTimestampSkew = Duration.millis(Long.MAX_VALUE);



    Builder(@Nullable String name) {

      this.name = name;

    }



    @Override

    public <InputLocalT> UsingBuilder<InputLocalT> of(PCollection<InputLocalT> input) {

      @SuppressWarnings("unchecked")

      Builder<InputLocalT, ?> cast = (Builder) this;

      cast.input = requireNonNull(input);

      return cast;

    }



    @Override

    public <OutputLocalT> EventTimeBuilder<InputT, OutputLocalT> using(

        UnaryFunctor<InputT, OutputLocalT> functor) {

      return using(functor, null);

    }



    @Override

    public <OutputLocalT> EventTimeBuilder<InputT, OutputLocalT> using(

		UnaryFunctor<InputT, OutputLocalT> functor, TypeDescriptor<OutputLocalT> outputType) {

      @SuppressWarnings("unchecked")

      Builder<InputT, OutputLocalT> cast = (Builder) this;

      cast.functor = requireNonNull(functor);

      cast.outputType = outputType;

      return cast;

    }



    @Override

    public Builders.Output<OutputT> eventTimeBy(

		ExtractEventTime<InputT> eventTimeFn, @Nullable Duration timestampSkew) {

      this.evtTimeFn = requireNonNull(eventTimeFn);

      this.allowedTimestampSkew =

          MoreObjects.firstNonNull(timestampSkew, Duration.millis(Long.MAX_VALUE));

      return this;

    }



    @Override

    public PCollection<OutputT> output(OutputHint... outputHints) {

      return OperatorTransform.apply(

          new FlatMap<>(name, functor, outputType, evtTimeFn, allowedTimestampSkew),

          PCollectionList.of(input));

    }

  }



  private final UnaryFunctor<InputT, OutputT> functor;

  @Nullable private final ExtractEventTime<InputT> eventTimeFn;

  private final Duration allowedTimestampSkew;



  private FlatMap(

      @Nullable String name,

      UnaryFunctor<InputT, OutputT> functor,

      @Nullable TypeDescriptor<OutputT> outputType,

      @Nullable ExtractEventTime<InputT> evtTimeFn,

      Duration allowedTimestampSkew) {



    super(name, outputType);

    this.functor = functor;

    this.eventTimeFn = evtTimeFn;

    this.allowedTimestampSkew = requireNonNull(allowedTimestampSkew);

  }



  /**

   * Retrieves the user defined map function to be applied to this operator's input elements.

   *

   * @return the user defined map function; never {@code null}

   */

  public UnaryFunctor<InputT, OutputT> getFunctor() {

    return functor;

  }



  /**

   * Retrieves the optional user defined event time assigner.

   *

   * @return the user defined event time assigner if specified

   */

  public Optional<ExtractEventTime<InputT>> getEventTimeExtractor() {

    return Optional.ofNullable(eventTimeFn);

  }



  /**

   * Retrieves maximal allowed timestamp skew.

   *

   * @return the user supplied maximal allowed timestamp skew

   */

  public Duration getAllowedTimestampSkew() {

    return allowedTimestampSkew;

  }

}